Current Issue

In May, cicada nymphs will appear by the handful
in areas treated to Brood II.

Nine years ago states bordering the Mississippi and those eastward
were treated to trillions of red-eyed insects known as Brood X periodical
cicadas. Like some strange biological equivalent of Haley’s comet, these
boisterous bugs were touted as a phenomenon that occurred only once every
seventeen years. This was a source of despair for those that loved them and a
source of relief for those that didn’t.

Part of the story not known to all, was that in other parts
of the country other broods of cicadas are found in intervening years. In fact,
there are 12 broods of 17 year cicadas and three broods of 13 year cicadas! So
it is with delight that we welcome Brood II to the east coast this year. After
seventeen years sucking sap from roots of trees underground, cicada nymphs are
getting ready to emerge from northern North Carolina to the Hudson Valley in
central New York. In the path of this biological deluge are major metropolitan
areas and their suburbs including Hartford, New Haven, New York City,
Philadelphia, and Washington, DC. One report has it that periodical cicadas may
even be seen in Central Park, NY.

One of the most precarious acts for the cicada
is shedding the exoskeleton it wore as a nymph.

The life of a cicada is mysterious and precarious. After
consuming xylem fluid from the roots of plants underground and completing their
juvenile life as nymphs, each cicada constructs an escape tunnel to the surface
of the earth. How do they know when seventeen years
have passed? One theory has it that they use annual fluxes in nutrients and
perhaps plant hormones as their zeitgebers. After tracking these changes for 17
years, their juvenile development is complete and they are ready to roll. But
to ensure that the world is green again and that temperatures are warm enough
to support escape from predators, feeding, flight, romance, and egg-laying,
they “listen” to the temperature of the soil. Soil temperatures in the middle sixties
are the cue that the world above ground is warm enough to support flight and
reproduction.

Escaping from a subterranean crypt appears to be a struggle for this nymph.

Be on the look out for the rare blue-eyed cicada.

Many nymphs emerge at night and make a mad dash for vertical
structures such as trees and shrubs. However, lampposts, street signs, and slowly
moving people seem to work just as well. After climbing up and away from the
soil, they attach to a firm object to begin the process of molting. Their outer
skin, or exoskeleton, splits along a predetermined line on their back and the
beautiful adult cicada wiggles free from the shell. The freshly molted adult is
almost pure white except for bright red eyes and patches of black behind the
head. Before its skin hardens, the cicada must expand its wings or it will be
unable to fly and seek a mate. After wings and legs have hardened, cicadas scurry
or fly to the treetops. Emergence from the earth and the final molt are perilous times
for cicadas. Many cicadas survive interment underground for seventeen years
only to perish attempting to molt or reach the safety of the trees.

A mad dash up the tree helps cicadas escape from ground
dwelling predators and join the big boy band in the treetop.

Males vibrate the tymbal to produce a variety of calls.

The big
noise in the treetops, the hallmark of periodical cicadas is all about love
baby, yeah. Male cicadas have evolved a unique structure called a tymbal. These
paired organs are located on the sides of their bodies just beneath the wings. Through
muscular contractions, males vibrate the tymbal much like a drumhead to produce
sound. Males produce a variety of calls for different purposes. If threatened
by a predator such as a bird or a squirrel, a loud squawking noise is made in
attempt to startle the predator and make an escape. The principal function of the tymbal is to produce calls
that assist in finding a mate and winning her affection. One type of call
attracts both males and females to a common assembly place such as a large
tree. When guys and gals get eye to eye, the male will use three distinct and
different courtship songs to try and convince the gal that he should be the
father of her nymphs. If the lady likes his advances, she will signal her
approval by flicking her wings with an audible click.

A
female (left) and male (right) enjoy a moment of rapture among the azalea
blossoms.

After mating, the female
cicada moves to tender young branches to lay eggs. Using a saber-like structure
on her abdomen called an ovipositor, the female gouges groves into the woody
tissue and lays 20 to 30 eggs in an egg nest. This process is repeated on one
or more plants, and a female may lay as many as 600 eggs total. After
incubating for more than a month, the eggs hatch and tiny nymphs a few
millimeters long dive to the earth beneath the tree. In a matter of minutes,
they burrow into the soil, find roots, and insert a small straw-like proboscis
into the roots. Cicada nymphs hunker down underground sipping sap and slowly growing
larger.

Females pump eggs into branches through a tube called an
ovipositor.

Small fruit trees can be damaged when females lay eggs in tender
branches.

Despite what you might have heard, cicadas are not blind. Their
red eyes see fine. They do not bite, although, if very thirsty, one may probe
you a bit with its tiny beak in search of moisture. Periodical cicadas are not
one species. Broods of 17 year cicadas are comprised of three distinct species
and 13 year brood contains at least four species.

With
more than 30 visible exit holes per square foot, one can see how there
could be almost 1 billion cicadas per square mile.

My friends in the Washington DC metropolitan area have asked
if they will enjoy cicadas this year. Alas, I fear that DC, Montgomery, and
Prince George’s are out of luck this time. According to historical records and
cicada experts, the nearest emergences of Brood II are likely to take place in
Calvert, Anne Arundel, St. Mary’s, Fairfax, and Prince William. Web sites
listed below have detailed maps of where Brood II will emerge in other states
along the east coast. Many mysteries remain concerning the evolution,
distribution, and synchronous appearance of cicadas. Without a doubt, they are
a true marvel of nature and one that should be enjoyed whenever possible.

References

This episode was inspired by John Zyla, our local cicada
guru, and the enthusiastic press corps tracking this amazing event. The
wonderful article by K. S. Williams and C. Simon “The ecology, behavior, and
evolution of periodical cicadas” was used as a resource for this episode.

To learn more about periodical cicadas and cicadas in
general, please visit the following excellent web sites: